Progress in thermodynamic analyses and optimizations for key component units in sea-based fuel synthesis systems

Abstract

This paper provides a brief introduction to the finite-time thermodynamic studies performed for chemical reaction processes. The research progress in the thermodynamic analyses and optimizations of the key component units in the two subsystems of the sea-based fuel synthesis system are described. This paper describes the component units in the carbon- and hydrogen-capture subsystems (i.e., the modules on the electrochemical acidification of seawater, extraction of CO2 in the acidic seawater, and production of hydrogen). This paper also describes the component units in the catalytic synthesis subsystems, which include the reverse water gas shift unit reactor and the Fischer-Tropsch synthesis unit reactor in the fuel synthesis technological pathway of long-chain hydrocarbon cracking; the subsystem also includes the CO2 hydrogenation of light olefins unit reactor and the olefins oligomerization unit reactor in the fuel synthesis technological pathway of short-chain hydrocarbon polymerization. Modeling and performance optimizations were performed, and the thermal design and optimization for the key component units of the sea-based fuel synthesis system were explored by combining the thermodynamics, heat transfer, fluid dynamics, chemical reaction kinetics, optimal control theory, and multiple-objective optimization methods. From shallow to deep, a one-dimensional plug-flow reactor model (with a completely temperature-controlled heat reservoir) and a two-dimensional pseudo-homogeneous reactor model (with a real heat reservoir) were established; high-temperature helium was employed as the heat carrier. From the reversible to irreversible models, the classical equilibrium thermodynamic model and finite-time thermodynamic model that considers various irreversible factors were established. From a single objective to multiple-objective optimizations, the optimizations were performed for single objectives, including the minimum entropy generation rate and minimum specific entropy generation rate (i.e., the entropy generation rate averaged by the production rate of target products), and multiple-objectives by comprehensively considering the production rate of the target products’ maximization and entropy generation rate minimization. The outlet mean conversion rate maximization and maximum radial temperature difference minimization were performed. Some results with important theoretical significances and application values were obtained, which can provide the scientific bases and theoretical guidelines for the design and optimization for the sea-based fuel synthesis systems. One of the important developmental trends was the constructal thermodynamic optimization for the two subsystems and the integration of the full sea-based fuel synthesis system with the component units.